Freeze protection device in heat pump system

ABSTRACT

A water source heat pump system having a plurality of zone air conditioning units, each unit adapted for selectively heating or cooling a zone independent of other units, each air conditioning unit having an air-to-refrigerant heat exchanger, a water-torefrigerant heat exchanger of the type having a water contact coil disposed within a housing, a refrigerant compressor, and refrigerant control means operable to selectively cause the airto-refrigerant exchanger to act as a refrigerant evaporator or condenser and the water-to-refrigerant heat exchanger to act as a refrigerant condenser or evaporator, the water-to-refrigerant heat exchanger and the air-to-refrigerant heat exchanger utilizing thermostat control means to control the operation of the air conditioning unit so as to prevent freezing of water in the water-to-refrigerant heat exchanger during the heating cycle and prevent frosting or freezing of condensate on the air side of the air-to-refrigerant exchanger during the cooling cycle.

United States Patent 191,

Cochran, Jr.

[11 3,823,572 July 16, 1974 FREEZE PROTECTION DEVICE IN HEAT [73] Assignee: American Air Filter Company, Inc.,

Louisville, Ky.

[22] Filed: Aug. 15, 1973 [21] Appl. No.: 388,421

Primary Examiner-William .l. Wye

57 ABSTRACT A water source heat pump system having a plurality of i zone air conditioning units, each unit adapted for selectively heating or cooling a zone independent of other units, each air conditioning unit having an airto-refrigerant heat exchanger, a water-to-refrigerant heat exchanger of the type having a water contact coil disposed within a housing, a refrigerant compressor, and refrigerant control means operable to selectively cause the air-to-refrigerant exchanger to act as a refrigerant evaporator or condenser and the water-torefrigerant heat exchanger to act as a refrigerant condenser or evaporator, the water-to-refrigerant heat exchanger and the air-to-refrigerant heat exchanger utilizing thermostat control means to control the operation of the air conditioning unit so as to prevent freezing of waterin the water-to-refrigerant-heat exchanger during the heating cycle and prevent frosting or freezing of condensate on the air side of the air-torefrigerant exchanger during the cooling cycle.

7 Claims, 2 Drawing Figures FREEZE PROTECTION DEVICE IN HEAT PUMP SYSTEM BACKGROUND OF THE INVENTION The invention relates to a water source heat pump system and more particularly relates to an air conditioning unit in a heat pump system utilizing a water-torefrigerant heat exchanger of the type having a water contact coil within a housing and an air-to-refrigerant heat exchanger with a thermostat control means disposed within the water contact coil and in contact with the air to monitor the temperature of water in the water contact coil and the refrigerant in the air-to-refrigerant exchanger.

Water source heat pump systems are those in which heat is injected into or extracted from flowing water, and the heat thus transferred is utilized indirectly to cool or heat air, by its application to a conventional refrigeration cycle. Generally, the air to be conditioned by a water source heat pump is confined to selected zones within an enclosed building, such as, for examunit to communicate with the water in the water source heat pump system. In utilizing the water in this manner, some air conditioning units may be heating while other air conditioning units may be cooling. In many cases,

- the means for transferring heat from the flowing water to the air conditioning unit is a water contact coil.

within a housing having a refrigerant therein such as a tube-in-tube heat exchanger orawater coil in a shell housing type heat exchanger. For example, in a tube-intube heat exchanger water flows through one tube and a refrigerant flows in the other with the heat being transferred according to the requirements of the air conditioning unit. If it is desired to put an air conditioner on a heating cycle where it is necessary to extract heat from the circulating water'in the tube-in-tube heat exchanger, the water in the tube-in-tube heat exchanger gives up heat to the refrigerant passing through the exchanger thereby reducing the temperature of the water passing therethrough. In some cases when atleast one unit is on the heating cycle, it has been found that the refrigerant entering the water-to-refrigerant exchanger is at a temperature below the freezing point of water and may reduce the temperature of the water in the water-to-refrigerant exchanger to its freezing point thereby stopping the flow of water through the exchanger and subsequently causing problems in the operation of the air conditioning unit. It has also been found that in some of these units when on the cooling cycle, refrigerant circulating through the air conditioning coil lowers the temperature of the air to a point wherein frosting or freezing of condensate on the air side of the air conditioning coil occurs. This causes reduction or complete stoppage of air flow, the result being a shut down on the unit. In order to overcome the problem of water freezing in the tube-in-tube exchanger, several arrangements have been proposed. However, none have been proposed to alleviate the water freeze up problem in the tube-in-tube exchanger and at the same time alleviate the problem of the frosting or freezing of condensate on the air conditioning coil.

SUMMARY OF THE INVENTION In the present invention, it is recognized that it is desirable to provide a means for preventing the freeze-up of water in a water coil within a refrigerant containing housing type heat exchanger wherein water is being utilized to transfer heat to the refrigerant during the heating cycle. Furthermore, it is recognized that it is desirable to provide a means for preventing the freeze-up of water in the water coil utilizing a temperature sensing device disposed at a position within the water stream of the water coil which is responsive in combination with thermostatic control means to a drop to a preselected temperature of the water in the coil, this temperature being above the freezing point of water during the heating cycle. Also, it is recognized that it is desirable to provide a means for preventing the frosting or .freezing of condensate on the air conditioning coil in an air conditioning unit.

The present invention advantageously provides a straightforward arrangement for the utilization of a temperature sensing device in a water coil within a refrigerant containing housingtype heat exchanger utilized in a water source heat pump system and an air conditioning coil in an air conditioning unit. The present invention further provides thermostat control means adapted to indirectly control the temperature of water in the water-to-refrigerant exchanger and the temperature of condensate on theair-to-refrigerant exchanger. The present invention also provides thermostat control means for preventing the freeze-up of water in a heat exchanger having a water coil therein and the frosting-up or freezing of condensate on an air conditioning coil in an air conditioning unit.

Various other features of the present invention will become obvious to those skilled in the art upon reading the disclosure set forth hereinafter.

More particularly, the present invention provides in a heating and cooling system for buildings, the system being operable to provide simultaneous and selective heating or cooling in a plurality of zones, the system having at least one air conditioning unit per zone, the air conditioning unit including reversible refrigeration machines which individually include a heat exchanger having a water coil therein, a refrigerant compressor, an air conditioning heat exchanger, and refrigerant control means operable to selectively cause the water coil type exchanger to act as a refrigerant condenser, and the air conditioning heat exchanger to act as a refrigerant evaporator; the improvement comprising: a temperature sensing device disposed within the water coil and in contact with an air conditioning heat exchanger; and, thermostat control means adapted to control the air conditioning unit when the temperature of the water'reaches a preselected temperature or the temperature of the condensate on the air conditioning heat-exchanging reaches a preselected temperature, the thermostat control means being operable in response to the temperature sensing device.

It is to be understood that the description of the examples of the present invention given hereinafter are not by way of limitation and various modifications within the scope of the present invention will occur to those skilled in the art upon reading the disclosure set forth hereinafter.

Referring to the drawing:

FIG. 1 is a schematic representation of a heating and cooling system for a building incorporating the invention; and,

FIG. 2 is an. enlarged schematic of a water-torefrigerant heat exchanger and air-to-refrigerant heat exchanger of FIG. 1 showing one preferred thermostat control means of the present invention.

In FIG. 1, a closed circuit heat pump system in a building having a plurality of zones is shown, only two zones identified as I and II being illustrated. Zone I is shown as being cooled and Zone II is shown as being heated. The closed circuit heat pump system includes a pump 2 for circulating water throughout the building including a plurality of zones or rooms which includes circulating air therein which is treated by individual air conditioning units within the room. A conduit 3 is disposed on the discharge side of the pump 2 connecting the pump 2 with a water inlet header 4, conduit 3 being the transferring means for water from pump 2 to header 4. The water inlet header 4 has a plurality of conduit branches extending therefrom, only two branches being exemplified, namely, branches 5 and 6. Each branch extending from the header 4 is adapted to communicate with the inlet water tube 26 of a tube-intube heat exchanger 8, tube-in-tube heat exchanger 8 being one example of a heat exchanger of the type having a water coil within a housing. The branch conduits 5 and 6 are adapted for transferring water from the header 4 to heat exchanger 8. An outlet water header is provided in the closed circuit as a means for returning water which has been subjected to heat treatment in the tube-in-tube heat exchanger 8 to a treating area in the closed circuit wherein the water will either be heated or cooled depending on the treatment necessary to maintain a heat balance within a preselected temperature range in the individual zones within the building. A heat reject heat exchanger 12 is incorporated within the circuit to remove heat from the circulating water, if the primary purpose of the system is to cool, whereas a supplementary heater 14 is incorporated if the primary function of the system is to heat the air within the zones. In FIG. 1, heat rejecting exchanger 12 and supplementary heater 14 are disposed in series with the header 10 and in communication therewith. It is to be realized that by-pass valving (not shown) may be incorporated around either exchanger 12 or heater 14, depending upon which unit is not needed in the closed system. Heat rejecting heat exchanger 12 may be any known type such as a water-to-water heat exchanger, a closed circuit evaporative cooler, or the like. Also, the supplementary heater 14 may be any known type of heat exchanger which adds heat to the water, such as a water-to-water heat exchanger, a boiler, or the like.

Each individual zone is to be treated by a separate air conditioning unit 16 therein which in turn is treated by the flowing water. Air conditioning unit 16 includes a motor driven compressor 18, a first heat exchanger 19 including an air conditioning coil 20 with refrigerant therein to condition the air and the water contact tubein-tube heat exchanger 8. A fan 24 is provided to draw air from the room and circulate it in heat exchange relation with the air-to-refrigerant exchanger 19. Motors, dampers, and controls for operating the fan 24 in combination with the heat exchanger 19 are well known in the art and are not shown in the figures.

The heat exchanger 8 is of the tube-in-tube type wherein water circulates through the inner tube 26 and refrigerant flows in the outer tube 28.

A reversing valve 30 is provided to control the direction of flow of refrigerant to the heat exchangers l9 and 8. The position of valve 30 in Zone I shows compressed refrigerant vapor fiowing from the compressor discharge 32 to the heat exchanger 8 wherein heat exchanger 8 is operating as a condenser. Thus, heat exchanger 19 is operating as an evaporator wherein air moving across the heat exchanger 19 gives up heat to the condensed refrigerant in the coil 20 and the air is therefore cooled thereby. In Zone II, valve 30 is positioned whereby the compressed refrigerant vapor from the compressor 18 is directed firstly to the heat exchanger 19 wherein heat exchanger 19 is operating as a condenser thereby adding heat to the air passing across the coil 20. The condensed refrigerant leaving the heat coil 20 is then subjected to treatment by the flowing water in the tube-in-tube exchanger 8 wherein the refrigerant absorbs heat from the flowing water in the tube 26.

An expansion device such as a capillary tube or expansion valve 34 is provided to separate the heat transfer zones of the two heat exchangers l9 and 8.

FIG. 2 illustrates one preferred arrangement of heat exchangers 8 and 19 of the present invention including thermostat control means for monitoring the temperature of'the water in tube 26 and condensate on the coil 20 and shutting down the air conditioning unit 16 in case the temperature of the water drops to'or below a preselected temperature or the condensate on coil 20 drops to a sufficiently low temperature to cause frosting or freezing of the condensate on coil 20. I

The tube-in-tube heat exchanger 8 includes an inner tube 26 which is disposed to communicate with the inlet water header 4 through branch conduit 9 at its outlet. An outer tube 28 is provided to communicate with refrigerant conduits 36 and 38. As noted in Zone I, when the air conditioning unit is on cooling, conduit 36 is an inlet conduit for the outer tube 28 and conduit 38 is an outlet refrigerant conduit. In Zone II, it is noted that when the air conditioning unit is on heating, conduit 38 is the inlet conduit and the outlet conduit for the refrigerant is conduit 36. It is realized that heat exchangers other than the tube-in-tube type may be used in the present invention, such as, for example, a water coil'disposed within a shell containing a refrigerant.

When the air conditioning unit is on heating, as mentioned above in the discussion of Zone II, there is considerable concern about the condensed refrigerant coming in through conduit 38 at such a low temperature that as it extracts heat from the flowing water in tube 26 it is possible to decrease the temperature of the water in tube 26 to its freezing point thereby stopping the flow of the water through the unit and causing considerable damage to the unit or else making the air conditioning unit ineffective. Therefore, a temperature sensing device 40 which may be, for example, a fluid filled capillary, a thermistor, thermocouple and the like is disposed within the inner tube 26 to a preselected position within the tube 26 to monitor the temperature of the flowing water at this preselected point.

In the present example, temperature sensing device 40 is a fluid filled capillary connected through a tube to a bellows 42 which is mechanically connected to an extension of a pivoted switch means 44. The arrangement is such that when the temperature of the'circulating water in the tube 26 drops to a predetermined temperature the switch means 44 opens the circuit which includes the electrical components identified by the number 50. The electrical components in 50 include at least the motor for the compressor 18. Thus, if the flowing water in the tube 26 drops to a preselected temperature, such as slightly above freezing, as soon as the water approaches or gets to this preselected temperature, the circuit including the compressor will shut down thereby allowing the water in tube 26 to return to its entering temperature thereby preventing the freeze-up of water within the tube 26. It is also realized that other factors may effect the opeation of the heat exchanger 8 besides the refrigerant at an extremely low temperature. For example, water flow in the head may be restricted by a plug in the line due to the inadvertent closing of a valve, the lodging of a piece of debris in the header line wherein the volume of water going to the exchanger will be diminished, or a pump may fail. In each case, the temperature sensing element will sense a drop in temperature within the heat exchanger where the water coil or tube is surrounded by refrigerant so that the drop in water temperature due to no fiow or a reduced flow will be sensed and the compressor will be stopped.

F IG. 2 further shows the temperature sensing device 40 is in contact with the outer surface of the air conditioning coil at a preselected number of positions along the coil 20. Thus, if the condensate on the coil 20 drops to a preselected temperature which would cause frosting or freezing on the surface of the coil 20, the fluid in the sensing device 40 will contract thereby decreasing pressure on the bellows 42 which in turn opens switch 44 de-energizing the circuit including the compressor 18 therein.

it will be realized that various changes may be made to the specific embodiments without departing from the principles and spirit of the present invention.

What is claimed is:

1. In a heating and cooling system for buildings, said system being operable to provide simultaneous and selective heating or cooling in a plurality of zones, said system having at least one air conditioning unit per zone, said air conditioning unit including reversible refrigeration machines which individually include a heat exchanger having a water coil therein, a refrigerant compressor, an air conditioning heat exchanger, and refrigerant control means operable to selectively cause said water coil type exchanger to act as a refrigerant evaporator and said air conditioning heat exchanger to act as a refrigerant condenser, or cause said water coil type exchanger to act as a refrigerant condenser and said air conditioning heat exchanger to act as a refrigerant evaporator; the improvement comprising: a temperature sensing device disposed within said water coil and in contact with an air conditioning heat exchanger; and, thermostat control means adapted to control said .air conditioning unit when the temperature of the water reaches a preselected temperature or the temperature of the condensate on the air conditioning heat exchanger reaches a preselected temperature, said thermostat control means being operable in response to said temperature sensing device.

2. The combination as described in claim 1 wherein said water coil is in the inner tube of a tube-in-tube exchanger and the outer tube contains a refrigerant therein. a

3. The combination as described in claim lwherein said water coil is the tube in a tube-in-shell exchanger and the shell contains a refrigerant therein.

4. The combination of claim I wherein said thermostat control meansis in electrical communication with said air conditioning unit whereby when water in said water coil reaches a preselected temperature, said air conditioning unit is de-energized.

5. The combination of claim 1 wherein said thermostat control means is in electrical communication with said refrigerant compressor I whereby when water in said water coil reaches a preselected temperature, said refrigerant compressor is de-energized.

6. The combination of claim 1 wherein said air conditioning heat exchanger includes an air conditioning coil with a refrigerant therein.

7. The combination of claim 6 wherein said temperature sensing device is in contact with the outer surface of said air conditioning coil at preselected points thereon. 

1. In a heating and cooling system for buildings, said system being operable to provide simultaneous and selective heating or cooling in a plurality of zones, said system having at least one air conditioning unit per zone, said air conditioning unit including reversible refrigeration machines which individually include a heat exchanger having a water coil therein, a refrigerant compressor, an air conditioning heat exchanger, and refrigerant control means operable to selectively cause said water coil type exchanger to act as a refrigerant evaporator and said air conditioning heat exchanger to act as a refrigerant condenser, or cause said water coil type exchanger to act as a refrigerant condenser and said air conditioning heat exchanger to act as a refrigerant evaporator; the improvement comprising: a temperature sensing device disposed within said water coil and in contact with an air conditioning heat exchanger; and, thermostat control means adapted to control said air conditioning unit when the temperature of the water reaches a preselected temperature or the temperature of the condensate on the air conditioning heat exchanger reaches a preselected temperature, said thermostat control means being operable in response to said temperature sensing device.
 2. The combination as described in claim 1 wherein said water coil is in the inner tube of a tube-in-tube exchanger and the outer tube contains a refrigerant therein.
 3. The combination as described in claim 1 wherein said water coil is the tube in a tube-in-shell exchanger and the shell contains a refrigerant therein.
 4. The combination of claim 1 wherein said thermostat control means is in electrical communication with said air conditioning unit whereby when water in said water coil reaches a preselected temperature, said air conditioning unit is de-energized.
 5. The combination of claim 1 wherein said thermostat control means is in electrical communication with said refrigerant compressor whereby when water in said water coil reaches a preselected temperature, said refrigerant compressor is de-energized.
 6. The combination of claim 1 wherein said air conditioning heat exchanger includes an air conditioning coil with a refrigerant therein.
 7. The combination of claim 6 wherein said temperature sensing device is in contact with the outer surface of said air conditioning coil at preselected points thereon. 